Manufacture of aliphatic acid anhydrides



June 27, 1933. s. J. GREEN ET AL 1,915,572

MANUFACTURE OF ALIPHATIC ACID ANHYDRIDES Filed Jan. 5, 1929 ll ll STANLEY J". GREEN RONALD. R. WIDDOWSON INVENTORS WcwM ATTORNEYS Patented June 27, 1933 UNETE PATENT oFFi'ce STANLEY JOSEPH GREEN AND RONALD RUMSEY WIDDOWSON, CF SPONIDON, NEAR DERBY, ENGLAND, ASSIGNQRS TO CELANESE CORPORATION OF AMERICA, A COR- PORATIQN OF DELAWARE MANUFACTURE OFALIPHATZC ACID ANHYDRIDES Application filed. January 5, 1929, Serial No. 330,576, and in Great Britain January 28, 1928.

This invention relates to the manufacture of aliphatic anhydrides from aliphatic acids.

periments when the acid vapour was passed in a rapid stream, small quantities (less than 2%) of acetic anhydride were obtained and the decomposition to hydrocarbons or other gaseous products was small, the major part of the acetic acid being recovered unchanged on condensation of the reaction vapours; with decreased speed ofpassage of the acetic acid vapours, however, no acetic anhydride was produced and very considerable quantities of gaseous decomposition'products (hydrocarbons, hydrogen, GO and CO were formed. It would seem from these experiments that in the case where acetic anhydride was produced with but small decomposition to gaseous products, the acid vapour was passed through the platinum tubes much too fastto allow it to attain a temperature of 1150 C., and that when, owing to slower passage of the acid vapour, the acid vapour was allowed to attain high temperatures, the reaction was more violent and the sole products of the reaction were gaseous products such as hydrocarbons, CO, CO etc. Our experiments have confirmed this View and we have found when passing acetic acid through platinum tubes in such manner that the acetic acid vapour attains a temperature of even 700 to 800; C. very considerable decomposition to gaseous products occurs. It is therefore evident that when Peytral produced acetic anhydride with but slight decomposition to gaseous products, the acetic acid vapour must only have attained a temperature below 700 to 800 C. 7

Following the publication of Peytral s eX- periments various proposals have been made, in particular in regard to catalysts for the reaction.

In our researches in this connection we have found that alkali metal tungstates are useless as catalysts for the reaction. We have found for instance thatsodium tungstate causes complete destruction of acetic acld vapour even at temperatures of about 500 C.

To have now made the surprising discovery that highly satisfactory results are obtained if the reaction is performed in the presence of a tungstic compound more acidic than an alkali tungstate (i. e. tungstic acid or tungstates other than alkali tungstates), and we have found that the following of such tungstic compounds are especially useful catalysts for the reaction :tungstates of calcium, magnesium or other alkali earth metals. w

According to the present invention therefore we produce aliphatic anhydrides (and especially acetic anhydride) by subjecting aliphatic acid vapour (and especially acetic acid vapour) to the action of heat in presence of a catalyst consisting of or comprising a tungstic compound more acidic than an alkali tungstate, and especially one or more tungstates of calcium, magnesium or other alkali earth metals.

If desired, the catalyst may be spread or deposited upon a filler or carrier such for instance as pumice (preferably granulated pumice stone), kieselguhr, carborundum or the like.

The process may be performed at temperatures of from about 400 to 700 (1., and preferably from about 550 to 650 C.

The acetic acid vapour, or other aliphatic acid vapour, may be subjected to the reaction in any suitable manner. Conveniently it may be passed in a rapid stream through any convenient form of apparatus (for instance one or more tubes or other reaction vessels) containing the catalyst and heated to the desired temperature. The tubes or other form of apparatus may be made of or lined with any suitable material, such for instance as fused silica, copper, gold, silver, graphite or certain alloy steels. Instead of heating the tubes or other form of apparatus the necessary heat may be applied directly to the catalyst, for instance, by heating the sameelectrically, and, as before mentioned, the catalyst may, if desired,'be deposited upon or spread upon fillers or carriers.

higher efficiency obtained.- It will, however,

be understoodthat we do not limit ourselves in regard to the pressure to be employed in the process.

The anhydride produced by the process may be separated and recovered from the reaction gases or vapours in any suitable way. In order to avoid hydrolysis and consequent loss of anhydride the vapours are preferably not submitted to simple condensation but are treated to separate the anhydride from the water vapour present or formed in the reaction. F or instance the gases or vapours from the reaction zone may be subjected to separation in the manner described in BritishPat'ent No. 303,772 of July 7, 1927 and in corresponding United States application S. No."

284,566 filed June 11, 1928, that'i'sto' say the anhydride may be condensed from the reaction vapours whilst carrying away the water by the vapour of one or more entraining liquids. In such form of execution thereaction vapours are preferably mixed after leaving vapour carried away with the vapours of the entraining liquid or liquids. Examples of entraining liquids which We may use for such method of condensation are, as indicated in the said British Patent No. 303,772 and correspondingUnited States application S. No. 284,566 file'dJune 11, 1928, benzene, carbon tetrachloride, petrol, mixtures of two or more of such bodies, or mixtures of ether and petroleum ether; it will be understood, however, as explained in the said British Patent No. 303,772 and corresponding United States application S. No. 284,566 filed 'June 11, 1928, that any other liquids chemically inert to the anhydride and having a, high entraining capacity for water may beemployed. The liquids should preferably have a low entraining capacity for the anhydride.

Or, for instance, the'reaction'vapours may be subjected to condensation by the method described in British Patent No. 298,667 of July 14, 1927, and corresponding United States application S. No. 285,613 filed June 15, 1928, that is to say they may be subjected to condensation by leading them under the surface of an extracting liquid cooled do W11 or otherwise kept at temperatures below (and preferablyconsiderably below the boiling point of water. As explained in the said British Patent N 0; 298,667 and corresponding United States a plication S. No. 285,613 filed June 15, 1928, by the term extracting liquid is meanta liquid or liquid mixture in which the anhydride is soluble and which is chemically inert to the anhydride and insolubleor substantially insoluble in water. As examplesof such extracting liquids may be mentioned benzene, chloroform and. mixtures' of ethyl ether or chloroform with one or more hydrocarbons such as light paralfins,

gasoline, kerosene, benzol or its homologues; as stated in the said British Patent No. 298,667 and correspondingUnited States application S. No. 285,613 filed June 15, 1928, it is preferable to use as extracting liquids, liquids of the character referred to which are themselves hydrocarbons or which contain hydro carbons, for example, benzene or mixtures of ethyl ether or chloroform with one or more hydrocarbons such as paraflins (particularly the petroleum fraction of boiling point 40 to (l'termed petroleum ether), gasoline (boiling point 709 to 90 (1), kerosene, benzol or its homologues, The following particular examples of extracting liquids are very suitable :ether in admixture with petroleum ether, chloroform mixed with petroleum ether and/or gasoline; and mixtures of ether and petroleum ether containing about 30 to 50% petroleum ether are especiall' suitable.

Or, or instance, the reaction vapours may be subjected to condensation by the method described in British Patent No. 310,863 of January 28, 1928, i. e. the reaction vapours maybe caused to impinge upon a flowing stream of benzene (or other water insoluble solvent for the anhydride) whereby said vapours are quickly cooled and condensed and the anhydride separated from the water. The benzene or the like so employed may be collected and the water layer (usually the lower layer, which separates out may be removed and'thebenzene (or equivalent) layer distilled to recover the anhydride.

' Or, for instance, the anhydride may be separated from the reaction vapours by the method described in British Patent No. 256,663 of April 9, 1925, and corresponding United States Patent No. 1,735,957, i. e. they may be subjected to fractional condensation immediately on leaving the hot reaction zone, for instance, they may be passed up one or more fractionating columns whereby the anhydride is condensedand the water allowed to pass on in vapour form.

It will of course be understood that in cases anhydride, preferably be passed through suitable apparatus (for instance, one or more reducing valves) wherein the pressure is reduced substantially to normal atmospheric pressure.

It will be understood that the invention is not limited as to the strength of aliphatic acid employed. The process can be performed even with the vapours of dilute acids; and besides affording a ready means for the manufacture of anhydrides from concentrated or highly concentrated acids, it affords valuable means for producing anhydrides from waste or dilute acids, especially waste or dilute acetic acids such as result from the acetylation of cellulose or other industrial acetylation processes.

' The following examples serve to illustrate someforms of execution of the process, it being understood'that they are given only by way of illustration and are in no way limitative..

Ewample 1 A highly useful catalyst for use in the present invention may be prepared as follows A solution of calcium chloride is mixed with a solution of sodium tungstate. The resulting precipitate of calcium tungstate is washed free from soluble compounds (such as sodium chloride) by repeated extraction with water. The catalyst so obtained is then dried and may be employed as such or spread upon a solid support such as granulated pumice.

E wample 2 Glacial acetic acid is boiled and the resulting vapours conducted in a rapid stream through a tube (composed of or lined with 7 copper, silver, gold or platinum) filled with the catalyst prepared in accordance with Example 1 (such catalyst being preferably spread upon granulated pumice stone) and heated to 550 to 650 C. The gases or vapours on leaving the tube are caused to impinge on a flowing stream of cold benzene whereby they are quickly cooled and condensed. The benzene stream is collected in e a suitable vessel and the water layer (usually the bottom layer) separated therefrom, and

' the benzene layer (usually the top layer) fractionally distilled to recover the acetic anhydride.

Example 3 A rapid current of carbon dioxide is passed through or over hot (or preferably boiling) acetic acid. According to the temperature of the acetic acid the carbon dioxide will become charged with a definite proportion of acetic acid vapour. The mixture of acetic acid vapour and carbon dioxide so obtained is then subjected to the reaction as in Example 2 and the anhydride recovered from the reaction gasesor vapours as in Example 2.

The accompanying diagrammatic drawing serves to illustrate a convenient form of apparatus for executing the invention in ac cordance with the above examples. For convenience the following description is given in terms of apparatus containing a particular constructional material and a particular catalyst, it is to be understood howeverthat other constructional materials or catalysts may, if desired, be employed.

Referring to the drawing, 1 is a tube composed of copper and filled with the catalyst 2, this catalyst being composed of calcium tungstate prepared in accordance with Example 1 and spread upon granulated pumice. 3 is a supply tanlccontaining benzene. 4 is a jacketed condensation vessel and 5 a receiver. In operationthe acetic acid vapour, or the mixture of acetic acid vapour is passed in arapid stream through the tube 1, this tube being heated to a temperature between 550 and 650 C. Froni the tube 1 the vapours pass via the pipe 6 to the condensation vessel 4;. Benzene is run from the supplytank 3 via the pipe 7 to the condensation vessel 4 across which vessel it passes in a rapid stream to the outlet pipe 8 which pipe is provided with a constant level overflow 9 serving to maintain a substantially constant level in the vessel 4. Perforated baflies 10 and 11 are provided in the vessel 4 to ensure even flow of the benzene 12 acrossthe vessel 4. The vessel 4 is cooled by the circulation of cold water or brine through the jacket 13 in such manner as to keep the benzene 12 in the vessel 4 at a temperature below 20 C. The reaction vapours leave the pipe 6 through the nozzle 14 which causes them to impinge in fine streams on to the stream of benzene 12 in the vessel 4:. The reaction vapours are condensed on coming into contact with the stream of benzene and the anhydride separated from the water to a very eflicient extent, the anhydride (together with any unconverted acetic acid) dissolving in the benzene whilst the water is condensed and separated. The benzene, together with the dissolved anhydride and separated water, passes via the constant level overflow 9 and the pipe 15 to the receiver 5 wherein the liquid separates into two layers, the water forming the lower layer whilst the benzene and dissolved anhydride (and unconverted acetic acid) form the upper layer. The anhydride can readily be recovered by distillation of the benzene layer.

Any uncondensable gases in the reaction vapours escape from the vessel 4- by the pipe 16 and gasses so escaping may be treated in any suitable Way to recover any anhydride carried over by them.

What we claim and desire to secure by Letters Patent is L a a a 1. Process for the manufacture of an aliphatic anhydride which-comprises thermally decomposing vapors of an aliphatic acid in presence of a catalyst comprising a tungsticv acidic than an alkali tungmore acidic than an alkali tungstate'.

3. Process for the manufacture of an aliphatic anhydride which comprises thermally decomposing the vapor of an aliphatic acid in "presence of an alkali earth metal tungstate.

4. Process for the manufacture of acetic anhydride which comprises thermally dey composing acetic acid vapor in presence of an alkali earth metal tungstate.

5. Process for the manufacture/of acetic anhydride which comprises thermally decomposing the acetic acid vapor'in presence of calcium tungstate; 7

6, Process according to claim 1 and wherein the reaction is performed at temperatures between 400 and 700 C.

7. Process for the manufacture of acetic anhydride which comprises subjecting the vapors of acetic acid to a temperature between 400 and 700 C. in presence of an alkali earth metal tungstate. i

8. Process for the manufacture of an aliphatic anhydride which comprises thermally decomposing the vapor of an aliphatic acid by passing said vapor in contact with a heat ed tungstlc compound more acidic than an alkali tungstate, supported upon a carrier.

1 upon a carrier.

9.7 Process for the manufacture of an aliphatic anhydride which comprises thermally decomposing the vapor of an aliphatic acid by passing said vapor in contact with a heated tungstlc compound more acidic than an alkali tungstate, supported upon granulated pumice. a a a 10. Process for the manufacture of an ali phatic anhydride which comprises thermally decomposing the vapor of an aliphatic acid by passing said vapor in contact witha heated alkali earth metal tungstate, supported 11. Process for the manufacture of an aliphatic anhydride which comprises thermally decomposing the vapor of an aliphatic acid by passing said vapor in contact with calcium tungstate, supported upona carrier.

12. Process for the manufacture of an aliphatic anhydride which comprises thermally decomposing the vapor of an aliphatic acid by passing said vaporin contact with calcium tungstate, supported upon granulated pumlce. v

13. Process for the manufacture of acetic anhydride which comprises thermally decomposing acetic acid vapor by passing said vapor in contact with calcium tungstate heated to 550650 0., supported mpon granulated pumice.

14. Process according to claim 1 and wherein the reaction vapors are treated to separate the anhydride from thewater vapor present therein.

In testimony;whereof we have hereunto subscribed our names.

STANLEY JOSEPH GREEN. RONALD RUMSEY WIDDOWSON. 

